Does anyone currently have both BOINC projects and F@H running concurrently?
 
I'm considering running both v7 and BOINC wrappered WCG at the same time.
 
Have there been any difficulties or workarounds needed for this set-up?

If you set it up right I don't see you having problems
 
What are your system specs?
 
are you considering running CPU and GPU or only one of them?
 

I'm running a full load of WCG Projects on my 2600K (OC'd @ 4GHz) + a 7622 GPU WU on my GTX580 right now.  I don't use V7 because I've always liked the FAH Console clients better.  But both FAH and WCG are running together just fine with no need to even scale back any of the CPU to make room for the GPU.  Both are running at the max (WCG getting all 8 threads of my CPU and the GTX580 running full bore too).

I've actually ran BOINC using 4 threads and folding smp with 4 threads together for a day....  I was reading some temperatures wrong and thought it was too hot, but it turned out I was just reading things wrong....  I still had the gpus running BOINC....  No real issues that I noticed....  
 
One thing though, when running a split set-up like this, it's better to either start both of them fresh or to at least make sure BOINC is running only on the number of threads you want before running both.  Even though BOINC can be suspended, some tasks will still run for a few after it to make sure the checkpoints are written.  I made the mistake of changing the number of threads and starting fah up before 4 threads in BOINC completely stopped and they got hung up....  

I'm going to use both CPU and GPU on a number of machines. (I don't want to give specs for all my rigs.) I am thinking of running v7 on GPU for F@H and CPU for BOINC-WCG. The idea of splitting processors for sharing CPU processing is interesting to me. How would that be accomplished?

The CPU's on the two rigs I have going are running WCG clients, the GPU's I have going are doing GPU-3 clients for Fold AT Home.
 
Using V.7 for the GPUs.

One way to split your CPU.
http://www.evga.com/forums/fb.ashx?m=1344677
Also, RHMash's warning above makes sense.  Get BOINC running on 50% before launching F@H.
 
I haven't actually tried this.  Because of the time-sensitivity of F@H's SMP work, I've been trying to go full-bore on one for 1/2 month then switch over completely to BOINC.

If you are planning on running that way - WCG on the CPU and F@H on GPU, I don't think you'll need to play with core affinities etc.
 
WCG tasks don't seem to load up the cpu when running 100% load the way F@H does. 
So there should be enough 'spare' cycles to feed the gpus without issue.
 
Something to note, GPU4 (adv-methods) units require less cpu cycles than gpu3, so might be worth trying.  As usual, remember that gpu4 runs very hot, so you need to set to stock speeds (unless you are under water) and aggressive fan profiles to keep the cards cool.